1. Field of the Invention
The present invention relates to a rubber composition having high adhesiveness to a metal, high modulus, high compression set resistance and high heat resistance, which enables the production of rubber/metal composite products to be used in the fields that require heat resistance and oil resistance. The present invention further relates to the composition can be suitably used for the products such as hoses, belts, tires, rolls and mold goods, and a producing method thereof. The present invention also relates to a hose having excellent adhesiveness between an inner tube and the like comprising the rubber composition and a reinforcing layer and excellent heat resistance. The present invention further relates to a rubber compounding agent that is easy-handling and improves heat resistance and modulus of a rubber, and a rubber composition containing the same.
2. Description of the Related Art
In recent years, many rubber products such as hoses, belts, tires, rolls and mold goods come to be used under high temperature and high pressure and also together with an oil heated for a long time, and deterioration of rubber products under such conditions always brings significant problems. If deterioration of rubber products is remarkable, very much time and labor are needed for maintenance or replacement of such deteriorated rubber products. Sometimes deterioration of rubber products may cause a large accident.
Conventional polymers that can be durable to continuous use under such high temperature (about 120-150xc2x0 C.) environment are acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), acrylic rubber (ACM), ethylene-acrylic acid ester copolymer rubber (AEM), ethylene-acrylic acid ester-vinyl acetate copolymer rubber (ER), ethylene-vinyl acetate copolymer rubber (EVM), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CM) and hydrogenated acrylonitrile-butadiene copolymer rubber (HNBR) obtained by hydrogenating a conjugated diene portion of acrylonitrile-butadiene copolymer rubber (NBR).
In general, in rubber compositions, it is known that an organic peroxide-crosslinked rubber composition using an organic peroxide has excellent heat resistance as compared with a sulfur-vulcanized rubber composition using sulfur in vulcanization.
However, the organic peroxide-crosslinked rubber composition does not generally contain sulfur that reacts with a metal for adhesion. As a result, such an organic peroxide-crosslinked rubber composition has poor adhesiveness to a metal surface and does not adhere to a brass that is plated on a metal surface. Therefore, rubber products composed of a combination of such an organic peroxide-crosslinked rubber composition and a metal such as a brass-plated steel plate have defects in that separation occurs at the interface between a rubber layer and a plated layer, resulting in breakage of the goods.
Diene rubber widely used in rubber products have excellent adhesiveness to a metal but do not have excellent heat resistance if sulfur in an ordinary amount is used as a crosslinking agent and an adhesive promoter is also compounded for improving adhesiveness to a metal. Further, where an adhesive promoter is not compounded, the amount of sulfur compounded is decreased that the ordinarily used amount and a vulcanization accelerator such as a sulfur donor is used together, for the purpose of improving heat resistance, heat resistance is improved but adhesiveness to a metal is decreased, resulting in impairing adhesiveness. Also, if an organic peroxide is used as a crosslinking agent for the improvement of heat resistance, heat resistance is excellent but adhesiveness to a metal is poor.
On the other hand, non-diene rubbers have excellent heat resistance and hence are used in various uses. However, non-diene rubber is difficult for vulcanization with sulfur, and it is necessary to crosslink with an organic peroxide or the like. In other words, since sulfur giving good adhesiveness to a metal cannot be used as a crosslinking agent, it is extremely difficult to directly adhere non-diene rubber to a metal. Various proposals have been made on formulation for developing adhesiveness. For example, JP-A-55-125155 describes that a polymer composition comprising an organic peroxide-crosslinkable polymer, organic peroxide, an epoxy resin and 2,4-dimercapto-6-R-1,3,5-triazine has a good adhesiveness to brass. From the results of our investigation and the contents of description in examples of the JP-A, it is presumed that the good adhesiveness is due to utilization of a reaction of chlorine in a chlorine-containing polymer such as chlorinated polyethylene with 2,4-dimercapto-6-R-1,3,5-triazine, a reaction of 2,4-dimercapto-6-R-1,3,5-triazine with an epoxy resin and a reaction of 2,4-dimercapto-6-R-1,3,5-triazine with copper in brass. However, since a reaction for adhesion does not occur in the case of chlorine-free polymers, there is a defect that such an adhesiveness does not sufficiently satisfy the adhesiveness in the level presently required.
For example, wires used as a reinforcing material of rubber hoses are generally high carbon steel wires, and in many cases, the wires are plated with brass to improve adhesiveness to a rubber.
However, where hydrogenated acrylonitrile-butadiene copolymer rubber (HNBR) or ethylene-acrylic acid ester copolymer rubber (AEM) such as ethylene-methyl acrylate copolymer rubber, having excellent heat resistance are used as, for example, an inner tube of a hose, those rubber are non-diene rubber which do not have unsaturated bonds in the main chain or side chains, and therefore sulfur cannot be used as a crosslinking agent. As a result, the non-diene rubber does not adhere to a reinforcing layer comprising reinforcing steel wires plated with brass.
Thus, regardless of diene rubber or non-diene rubber, rubber is demanded to overcome the above-described problems and to satisfy both adhesiveness to a metal and heat resistance.
Further, from the point of light-weight of rubber compositions, demand for high rigidity of rubber compositions is increasing, and rubber compositions having high modulus are demanded. There are various techniques to improve modulus of rubber compositions but on the other hand, there is disadvantage of impairing other physical properties, particularly heat resistance. Thus, it is necessary to optimize the physical properties in every rubber composition while balancing the physical properties.
Crosslinking aids have conventionally be used in rubber compositions crosslinked with organic peroxide to improve modulus (ex. stress at 100% elongation). Bifunctional or multifunctional polymerizable monomers are generally used as the crosslinking aids. Of those, triallyl isocyanurate (TAIC) and triallyl cyanurate (TAC) are known as having high efficiency of co-crosslinking and particularly high effect to improve modulus. However, triallyl isocyanurate has a melting point in the vicinity of 25xc2x0 C. and triallyl cyanurate has a melting point in the vicinity of 27xc2x0 C. Therefore, there are the disadvantages that those compounds are liquid if temperature is high, which are difficult to mix with a solid material, and those compounds are solid if temperature is low, which are also difficult to mix with a solid material, thus handling properties are poor. It is thus desired to overcome those problems.
Further, where TAIC and/or TAC and silica are used together, handling properties not only TAIC and/or TAC but also silica become problem in many cases. Specifically, since silica has a strong hydrophilicity, there is the problem that it is difficult for silica to be uniformly dispersed in the case of mixing with a hydrophobic material, and there is also the problem that silica is scattered in air in working because of the bulkiness thereof.
On the other hand, there are many cases that organic peroxide-crosslinkable rubber compositions, particularly organic peroxide-crosslinkable rubber compositions comprising a polymer in which the main chain is a methylene chain, as the main component of a raw material rubber are used for rubber compositions requiring high heat resistance.
However, if TAIC and/or TAC are used in large amount in the rubber compositions comprising a polymer in which the main chain is a methylene chain, as the main component of a raw material rubber in order to impart high modulus, those do not contribute to co-crosslinking, thereby increasing the proportion of the self-curable rubber components. As a result, the inherent heat resistance of rubber compositions is impaired and in addition, breakage strength such as tear strength or tensile strength deteriorates. Thus, it was practically impossible to make modulus remarkably high by adding a large amount of TAIC and/or TAC.
Therefore, a compounding agent for rubber that does not impair heat resistance and can realize high modulus is desired regarding the organic peroxide-crosslinkable rubber compositions comprising a polymer in which the main chain is a methylene chain, as the main component of a raw material rubber.
Accordingly, one object of the present invention is to provide a rubber composition that has high adhesiveness to a metal (brass), high modulus, high compression set resistance and high heat resistance and due to those properties, can suitably be used in composite products of a rubber and a metal, such as hoses, belts, tires, rolls and molded products.
Another object of the present invention is to provide a process for producing the rubber composition that exhibits adhesion stability of the rubber composition.
Still another object of the present invention is to provide a hose having excellent heat resistance, durability and the like in which a reinforcing layer comprises a reinforcing steel wire plated with brass and the rubber composition is used as an inner tube material that adhesiveness between the inner tube and the reinforcing layer is excellent and heat resistance, modulus and compression set resistance are particularly good.
Further object of the present invention is to provide TAIC and/or TAC supported on silica, used in a compounding agent for a rubber, having good handling properties, and a compounding agent for a rubber, comprising the same.
Still further object of the present invention is to provide a rubber composition having improved modulus while maintaining high heat resistance by using the compounding agent in an organic peroxide-crosslinkable non-diene raw material rubber composition, particularly a rubber composition containing a polymer having a methylene chain as the main chain.
According a first embodiment of the present invention, there is provided a rubber composition comprising:
(1) 100 parts by mass of a raw material rubber, with the exception of a copolymer rubber having an iodine value of 15 or less, having in a polymer chain 10 to 45% by mass of a unit portion from an unsaturated nitrile (Y portion; VCN), 0 to 5% by mass of a unit portion from a conjugated diene (Z portion; Cxe2x95x90C) and 90 to 50% by mass of a unit portion obtained by hydrogenating a unit portion from a unit portion from an ethylenically unsaturated monomer other than the unsaturated nitrile and/or a unit portion of the conjugated diene (X portion; Cxe2x80x94C);
(2) 0.1 to 15 parts by mass of 2,4-dimercapto-6-substituted-1,3,5-triazine represented by the following formula 1: 
xe2x80x83wherein R represents a group selected from the group consisting of mercapto group, alkoxyl group, monoalkylamino group, diaklylamino group, monocycloalkylamino group, dicycloalkylamino group and N-alkyl-N-arylamino group; and
(3) 1 to 100 parts by mass of a polymer having epoxy groups crosslinkable with the raw material rubber.
Preferred embodiments in the first embodiment are as follows.
Preferred rubber composition of the present invention is an organic peroxide-crosslinkable raw material rubber, with the exception of a copolymer rubber having an iodine value of 15 or less, having in a polymer chain 10 to 45% by mass of a unit portion from an unsaturated nitrile (Y portion; VCN), 0 to 5% by mass of a unit portion from a conjugated diene (Z portion; Cxe2x95x90C) and 90 to 50% by mass of a unit portion obtained by hydrogenating a unit portion from a unit portion from an ethylenically unsaturated monomer other than the unsaturated nitrile and/or a unit portion of the conjugated diene (X portion; Cxe2x80x94C), and the polymer having epoxy groups is an organic peroxide-crosslinkable polymer.
Preferred rubber composition of the present invention is that the organic peroxide-crosslinkable raw material rubber is a diene rubber.
Preferred rubber composition of the present invention is that the organic peroxide-crosslinkable raw material rubber is a non-diene rubber, with the exception of a copolymer rubber having an iodine value of 15 or less, having in a polymer chain 10 to 45% by mass of a unit portion from an unsaturated nitrile (Y portion; VCN), 0 to 5% by mass of a unit portion from a conjugated diene (Z portion; Cxe2x95x90C) and 90 to 50% by mass of a unit portion obtained by hydrogenating a unit portion from a unit portion from an ethylenically unsaturated monomer other than the unsaturated nitrile and/or a unit portion of the conjugated diene (X portion; Cxe2x80x94C).
Preferred rubber composition of the present invention is that the organic peroxide-crosslinkable raw material rubber is at least one member selected from the group consisting of ethylene-acrylic acid ester copolymer rubber, ethylene-acrylic acid ester-vinyl acetate copolymer rubber and ethylene-vinyl acetate copolymer rubber.
Preferred rubber composition of the present invention is that the organic peroxide-crosslinkable raw material rubber is selected from the group consisting of ethylene-propylene copolymer rubber and/or ethylene-propylene-diene copolymer rubber.
Preferred rubber composition of the present invention is that the organic peroxide-crosslinkable raw material rubber is selected from the group consisting of chlorinated polyethylene rubber and/or chlorosulfonated polyethylene rubber.
Preferred rubber composition of the present invention is that the diene rubber is acrylonitrile-butadiene copolymer rubber.
Preferred rubber composition of the present invention is that the raw material rubber is a sulfur-crosslinkable raw material rubber, and the polymer having epoxy groups is a sulfur-crosslinkable polymer.
Preferred rubber composition of the present invention is that the raw material rubber an d the polymer having epoxy groups are a raw material rubber having epoxy groups.
Further preferred rubber composition of the present invention is that the raw material rubber having epoxy groups is acrylic rubber containing a monomer having epoxy groups as a copolymerizable component.
Further preferred rubber composition of the present invention is that the rubber composition further comprises 0.1 to 30 parts by mass of at least one member selected from the group consisting of triallyl isocyanurate and triallyl cyanurate.
Further preferred rubber composition of the present invention is that the rubber composition further comprises 1 to 50 parts by mass of silica.
According to a second embodiment of the present invention, there is provided a process for producing a rubber composition comprising:
(1) 100 parts by mass of an organic peroxide-crosslinkable raw material rubber;
(2) 0.1 to 15 parts by mass of 2,4-dimercapto-6-substituted-1,3,5-triazine represented by the following formula 1: 
xe2x80x83wherein R represents a group selected from the group consisting of mercapto group, alkoxyl group, monoalkylamino group, diaklylamino group, monocycloalkylamino group, dicycloalkylamino group and N-alkyl-N-arylamino group; and
(3) 1 to 100 parts by mass of a polymer having organic peroxide-crosslinkable epoxy groups; and
(4) 1 to 10 parts by mass of organic peroxide, which comprises maintaining a temperature of a mixture at 140xc2x0 C. or lower through the overall steps of from mixing the raw material rubber with at least one of the remaining components to mixing all the components.
Preferred embodiment in the second embodiment is as follows.
Preferred process for producing the rubber composition of the present invention is that temperature of the mixture in the steps after addition of the 2,4-dimercapto-6-substituted-1,3,5-triazine is 100xc2x0 C. or lower.
According to a third embodiment of the present invention, there is provided a hose comprising a rubber composition which comprises:
(1) 100 parts by mass of an organic peroxide-crosslinkable raw material rubber;
(2) 0.1 to 15 parts by mass of 2,4-dimercapto-6-substituted-1,3,5-triazine represented by the following formula 1: 
xe2x80x83wherein R represents a group selected from the group consisting of mercapto group, alkoxyl group, monoalkylamino group, diaklylamino group, monocycloalkylamino group, dicycloalkylamino group and N-alkyl-N-arylamino group; and
(3) 1 to 100 parts by mass of a polymer having organic peroxide-crosslinkable epoxy groups; and
(4) 1 to 10 parts by mass of an organic peroxide.
Preferred embodiments in the third embodiment are as follows.
Preferred hose of the present invention is that the raw material rubber in the rubber composition forming the inner tube and/or outer cover is a copolymer rubber having an iodine value of 15 or less, having in a polymer chain 10 to 45% by mass of a unit portion from an unsaturated nitrile (Y portion; VCN), 0 to 5% by mass of a unit portion from a conjugated diene (Z portion; Cxe2x95x90C) and 90 to 50% by mass of a unit portion obtained by hydrogenating a unit portion from a unit portion from an ethylenically unsaturated monomer other than the unsaturated nitrile and/or a unit portion of the conjugated diene (X portion; Cxe2x80x94C).
Preferred hose of the present invention is that the raw material rubber in the rubber composition forming the inner tube and/or outer cover is ethylene-acrylic acid ester copolymer rubber (AEM).
Preferred hose of the present invention is that the inner tube comprises a rubber composition containing the HNBR, and the outer cover comprises a rubber composition containing the AEM.
According to a fourth embodiment of the present invention, there is provided triallyl isocyanurate and/or triallyl cyanurate supported on silica, comprising 30 to 80% by mass of isocyanurate and/or cyanurate and/or their oligomers and 70 to 20% by mass of silica, the isocyanurate and/or cyanurate is obtained by heat treating triallyl isocyanurate and/or triallyl isocyanurate in the presence of silica.
According to a fifth embodiment of the present invention, there is provided a compounding agent for a rubber, comprising the triallyl isocyanuarate and/or triallyl cyanurate supported on silica.
According to a sixth embodiment of the present invention, there is provided a rubber composition comprising:
(1) 100 parts by mass of an organic peroxide-crosslinkable raw material rubber;
(4) 1 to 10 parts by mass of an organic peroxide; and
(5) 0.5 to 100 parts by mass of the compounding agent for a rubber.
Preferred embodiment in the sixth embodiment is as follows.
Preferred rubber composition of the present invention is that the raw material rubber mixed with the compounding agent for a rubber is a polymer in which the main chain is a methylene chain.